Generally, a multistage amplifier includes a plurality of amplifiers connected in cascade such that an initial input signal is amplified by passing through several amplifiers. In this case, an output of a preceding amplifier becomes an input of a following amplifier and an output of the following amplifier becomes an input of the next amplifier, and so on.
Each amplifier included in the multistage amplifier may be formed of a preamp or a comparator using a differential amplifier. The multistage amplifier may be formed by connecting the preamps or the comparators in cascade.
A number of applications are available for a multistage amplifier to various electronic devices. An analog-digital converter is one such device that employs a multistage amplifier. For instance, an analog-digital converter may have a plurality of amplifiers that are connected in an open-loop structure in which there is no feedback for high-speed operation.
Where an analog-digital-converter employs a multistage amplifier, effects caused by mismatch, offset, and glitch in a comparator, which is the very end terminal, may be reduced by using a gain of each amplifier. Furthermore, a higher resolution of the analog-digital converter may be achieved where a multistage amplifier is used instead of a single amplifier.
However, in the case of using a plurality of amplifiers, the overall operation speed may become slower due to delay of each amplifier. Since the analog-digital converter may compare an input signal to a reference signal to detect a zero-crossing point using a comparator, and then encode a value corresponding to the detected zero-crossing point to obtain a digital output, the overall performance of the analog-digital converter may depend on how fast and accurately each amplifier is settled at the zero-crossing point.